


Undertail Collection

by Godheadharley



Category: Undertale (Video Game)
Genre: Biting, Dom/sub Play, Finplay, Multi, One Shot Collection, Other Additional Tags to Be Added, Skeletons, Smut, Teasing, Vaginal Fingering, boneplay
Language: English
Status: In-Progress
Published: 2015-11-23
Updated: 2015-11-23
Packaged: 2018-05-03 02:47:42
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 2
Words: 2,951
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/5273630
Author URL: https://archiveofourown.org/users/Godheadharley/pseuds/Godheadharley
Summary: <blockquote class="userstuff">
              <p>A continuing collection of one-shot Undertale smut fics. Requests welcome.</p>
            </blockquote>





	1. Sans/Reader Teasing Boneplay

**Author's Note:**

> I figured it would be a shame to keep all this sinning just to myself. Enjoy this continuing collection of one-shot smut fics and feel free to send me requests. Please leave comments and kudos to show your support!

If there’s one thing you’ve learned about Sans since you two started dating it’s that he’s incredibly lazy. At first you’d wondered why he’d chosen to keep living with his brother after monsterkind was freed from the underground. Wouldn’t he prefer to make a life for himself up here? However, the more time you spent in the house, the more obvious it became that he relied on Papyrus for nearly everything. Though he managed to pay a good portion of the bills - how he did that was always a mystery - every ounce of housework was left for the taller brother in his off-time. Well, until recently, that is. 

Your presence had started small: a few hours at the house for a game and maybe the occasional night over, though you’d always be out early the next morning. But as time droned on, you became more familiar, spending a few nights a month and then a few nights a week. Now you spent more time here than at your actual home. You’d tried bringing up the subject of rent, but Papyrus was having none of it. He enjoys you being around, and the effect you have on his brother is nice too. Instead, you earn your keep by doing all of the housework: washing dishes, doing laundry, cleaning, etc. At least a few hours a day is devoted to these tasks. 

And today is like any other. You arrive after work, around six in the evening, grab a quick shower, and plot what to do for the rest of the day. Papyrus will be out late training with Undyne. Sans is taking a nap on the couch, having arrived home shortly before you. If you remember correctly, he will be home for the rest of the day. Maybe, you think, you'll catch a movie tonight, if you can motivate him to go out. Now, however, you’ve decided to do the dishes. 

You tie on the apron that hangs on the pantry door. It’s a little long on you, and a little short on Papyrus, but it gets the job done. It had originally read ‘Number One Dad’, but Papyrus had altered it to read ‘Number One Cool Skeleton’ with embroidery. He is surprisingly talented with a sewing machine, at least when he isn’t accidentally sewing his glove to whatever he’s working on. After that you pull on a pair of pink kitchen gloves and get to work rinsing the dishes and loading them into the dishwasher. 

From the living room you can hear Sans groan and wake, then the plodding of his slippers on the hardwood floor. He enters the kitchen rubbing his eye sockets and heads for the fridge as he grumbles. Inside he finds a new bottle of ketchup and pops the top to take a hearty squeeze, then begins to retreat to the couch. 

“Good morning, lazy bones,” you call after him. 

“huh?” murmurs, looking up towards the clock in the living room. 

“It’s still Friday,” you tease, turning off the sink. “Hey, do you want to go see the new Mettaton movie tonight?”

He shrugs. 

“Okay, better question, _will you_ go see it tonight?”

“pretty tired,” he replies, yawning. Even now there’s a grin plastered on his face, and it’s still hard to tell just what he’s feeling despite months together. 

“maybe next week,” he grunts, then plops back down on the couch.

You sigh, then get back to scrubbing. Maybe this is best, he must be so tired from working constantly. He might be lazy to a fault but he never hesitates when there’s sufficient motivation, like keeping the power on or making sure no one comes to repossess Papyrus’s car. 

Actually, now that you think about it, there may still be a way to see that movie tonight.

You finish up quickly and start the dishwasher before returning the apron and gloves to their rightful place and joining Sans on the couch. He’s now turned on the TV, but seems generally disinterested and instead bobs in and out of consciousness. As you take your seat next to him, he rouses a bit. 

“That's fine,” you state, “we can always see it some other time.”

Try as you might, you are unable to prevent a mischievous thread from lacing in with your words. Sans doesn’t seem to notice, or at least doesn’t react. Making the first move, you casually fling your arm around his shoulders and pull him in. He settles his head on your chest and focuses on the screen. The MTT channel is doing some special documentary about Mettaton’s life before becoming a star in the overworld, hosted by the robot himself. They show Alphys’s lab where he claims to be born, the resort where he still has one employee, and the various sets from which he originally broadcasted. 

As both of you stare straight ahead, your hand begins to wander. First you sweep over San’s smooth skull. If he had hair, your fingers would be running through it right now, but instead you rake your fingertips over the smooth bones, tapping your nails gently. His breath falters a little bit. He’s taken notice. Next, you fingers dip to far side of his neck, running along the curves and juts of each section. He shivers in response, hands clenching into fists in his pockets. He must know your game by now, but he’s enjoying it too much to comment. Your hand draws up to the first cervical vertebra at the base of his skull and you stroke it gently. He shudders and lets out a moan, eye sockets now shut tightly. You know just where to touch to get him excited. 

You smoothly swing your leg over and turn to straddle him, digits still occupied on his neck. His own hands quickly snake into your clothes and find purchase on your hips, gripping them tightly. Every flutter of your fingers makes his own twitch, leaving curious impressions on your skin. You use your free hand to unzip his jacket and push up his tee shirt to reveal his rib cage. Before you started dating, this sight might have freaked you out a little bit. Now, however, you’re starting to get turned on. 

You run your hands over his ribs, giving each one special attention. Now, Sans’s head is thrown back on the couch and his grin is bigger than ever. You work from the top to the bottom, making sure no curve or bump goes untouched, floating to the next rib only when you reach the terminus at the spine or sternum. When you finally reach the end of Sans’s ribcage, his hold of you lessens and his entire body relaxes a bit. But you’re by no means done. 

Your hands snake up into the inside of his ribcage and you’ve barely touched one bone before Sans is moaning loudly and bucking into you. The air is filled with sparks of blue magic prickling on your skin and collecting beneath your hips. His shorts start to bulge and your face is flush with arousal. You knew this would be fun, but not _this_ fun. You continue your incursion undeterred, pressing harder now and scratching at the inside of his ribs with your nails. The sounds erupting from his mouth are high and ragged and he’s biting the space where his lip would be in an attempt to stay quiet. 

Your fingers come to rest just beside the inside of his spine, the most sensitive part of his body. You extend just one finger and brush it ever so gently against the column, around the tenth thoracic vertebra. His entire body locks up at the touch, fingers digging into your skin, dead still. You can hear him try to choke in a breath over the sound of the television, but even that is a struggle. He releases a whine and his jaw shakes as he attempts to speak. 

“f-f-fuck me,” his voice is shakier than you’ve ever heard it, “p-pleasssse.”

You remove your hands from his bones and he collapses back into the cushions. He’s panting and heaving like he just ran a marathon, twitching and curling his fingers and limbs. You dismount and he whimpers, waiting for you to disrobe. 

But you don’t. 

You walk over towards the door and begin to slip on your shoes. Sans blinks for a moment, confused as to what you could possibly be doing. 

“You know,” you begin, stealing the chance to speak before he can muster any words, “I really wanted to see that movie tonight. I’m just too distracted to do anything else right now. But maybe after-”

In an instant he’s on his feet. Without another word, he grabs your hand and rushes for the door. You smile, satisfied that you’ve discovered a shortcut to San’s motivation.


	2. Alphys/Undyne Sensitive Fins

**Notes for the Chapter:**

> Done as a request for tarafyingcarrot. I had a lot of fun with this one despite being less familiar with the characters. Keep those comments and requests rolling in! I have quite the list now but I hope to work through them all. Enjoy!

Undyne, being the incredibly important and busy woman that she is, keeps an appropriately tight schedule. Classes to teach from eight to two every weekday, then coaching practice until six at night. Multiple games every weekend. Cooking lessons with Papyrus Tuesdays and Thursdays til nine. Eight hours of sleep a night to keep her well-rested, and training almost every waking hour that isn’t otherwise already taken. Even though she shares a home, and bed, with Alphys, it seems like a miracle any time the two can sit down for some personal time together. 

But occasionally, when the stars align, the two can find themselves alone without distraction. Luckily, this is one of those nights. 

They’ve just spent the last hour watching the Mew Mew holiday special OVA, the one Alphys spent months trying to find on obscure anime swap boards. She’d finally tracked down a copy and traded away one of her rare misprint figures for it. Now her prized possession lives on the shelf among the other titles, brought out only for the occasional viewing. This was Undyne’s first time watching, much to Alphys’s excitement. 

However, Undyne had spent much of the run-time lying with her head on the armrest, trying not to fall asleep. Normally, she would be sitting up and yelling at the characters to kiss or fight or both, but today she was exhausted, totally burnt out after a long week. In fact, the only reason she was here right now was the presence of thunderstorms that canceled practice. It was rare for her to show such vulnerability, especially around other people, but Alphys was one of few she trusted enough to see her off her game. Still, this lack of enthusiasm worried Alphys so much she could barely focus on the show. 

Now they’re lying in bed, Undyne stripped down to her tank top and panties and Alphys clad in a pair of fish-patterned pajamas, gifted to her, obviously. Her head rests on Undyne’s chest as the pair lie quiet, the sound of rain filling the room as drops hit the window. 

“Undyne?” Alphys starts nervously. 

“Yeah?” 

“A-are you alright?”

“What? Yeah, of course!” She laughs, but quickly trails off. 

“Okay,” Alphys concedes, frowning. 

Undyne is always working so hard, Alphys thinks. But what does _she_ do all day? She just sits are her computer watching anime and browsing fan art online. Occasionally, Mettaton stops in for repairs, but other than that, her talents go to waste. And what does Undyne do? She goes out and spends all of her time pushing her limits: putting in more hours at work, encouraging Papyrus to learn new recipes, bench-pressing more children. The guilt of not living up to the same standard weighs on Alphys’s mind. It wouldn’t be possible for her to do all that; the stress would destroy her. But maybe she can make up for it in another way.

“Hey, U-Undyne? Do you think we could maybe, well, you know…”

“I’m too tired, Alphie.”

“U-uh, you wouldn’t really have to do anything, I could just-”

“You want to top ME?” 

Undyne lets out a hearty chuckle as Alphys goes red with embarrassment. This is a total mistake, a horrible idea, she thinks. 

“Nevermind, that was really stupid, I shouldn’t-”

“You have my attention,” Undyne purrs. 

Well, now there’s no choice. 

“O-okay, but you have to cl-close your eyes,” Alphys stumbles out nervously. 

Undyne puts on her typical mile-wide grin and obeys as Alphys shifts to straddle her hips. Her hands are shaking and she’s face is burning hotter than Grillby’s, but this is happening. She has to do this, has to do something to make up for all the time she’s wasted while Undyne is out being so important. If she can’t even do this, how can she expect Undyne to put up with her? Wait, why does Undyne put up with her at all? She’s so useless, so unimportant, so-

Alphys completely locks up. 

After a minute of silence and stillness, Undyne opens her eyes to see Alphys with her face in her hands. 

“Whoa! Hey, calm down, what’s wrong?” 

“I just, I can’t, you’re so great and I’m so terrible, and this is so-”

“It’s okay, slow down.”

Alphys inhales deeply before continuing. 

“I just want to help you relax. You do so much and I don’t do anything at all.”

“What? That’s not true! You do lots of stuff! You make all kinds of neat gadgets and you know all the best anime and you even cook sometimes!” 

“But you’re so much better than me at everything.”

“Pfff, no way! All I can do is beat people up. You’re the one with all the smarts. You even made Mettaton, and now he’s, like, the biggest star in the world! All because of you.”

Alphys smiles a bit. 

“You’re so hard on yourself all the time,” Undyne continues, “but really you’re awesome. I wouldn’t be here if that wasn’t true.”

“Thanks,” Alphys mumbles, squeezing her hands together restlessly. 

“And you don’t have to do this if you don’t want to.”

“No!” She blurts out. “I… I want to. You just have to promise not you laugh at me if I mess up.” 

“Of course,” Undyne replies, leaning up to plant a kiss on her girlfriend’s nose before closing her eyes again. 

Again red as a flame, Alphys steadies her hands and prepares. She’s been thinking about this moment for hours, planning what to do, but every note has fled from her mind. It’s just like in hentai, she thinks, go for the kill. 

Slowly, she cups her hands on either side of Undyne’s face and leans in for a kiss. Undyne reciprocates, fighting the urge to take control and move faster. Her style of romance is a lot faster and rougher. Their teeth clink and Alphys pulls away to catch her breath before leaning down again and locking lips with her partner. Undyne’s teeth are sharp and unrelenting as she nibbles on Alphys’s lip and curls her tongue around her lover’s. At this distance, the heat coming from Alphys’s face is noticeable and only serves to fire her up more. 

With a jittery hand, Alphys reaches over and gently strokes one fin jutting from Undyne’s cheek, and her partner’s breath hitches instantly. 

“D-do that again,” Undyne demands with a moan. 

Alphys once again draws a claw along the fin, eliciting a long, high keen. Undyne grabs Alphys’s thigh and clutches tightly, digging her nails into the other’s golden skin. Alphys continues, taking a ray between each finger and drawing outwards. Beneath her, Undyne tenses with each motion, letting out sounds quite unfit for a former head of the royal guard. 

Feeling emboldened, Alphys dips her free hand lower towards Undyne’s panties, but pauses at the waistband. 

“I-is this okay?” She asks. 

“Hell yes!” Undyne responds, one hand clutching the sheets while the other leaves claw marks on her lover's thigh. 

Alphys resumes, reaching in to caress Undyne’s folds. She’s already dripping wet straining up to meet Alphys’s touch. The sense of being in control is foreign but arousing for the newly-minted domme, and she wastes no time in slipping one finger inside while her thumb works Undyne’s clit. Her other hand scratches gently on the backside of the left fin. She starts pumping faster, slipping in another finger as Undyne’s moans fill the room. 

“ _Ngh, fuck!_ ” Undyne is starting to lose it. Her claws rip through the sheets. 

Alphys is thrusting harder, even though her hand is starting to cramp. Hearing Undyne’s breathing become labored is really driving her wild. Being in control is so much better than she thought it would be. To see Undyne squirm and cry by her own hand is intoxicating. 

“I-I’m gonna-”

Alphys leans forward and takes the edge of one fin in her mouth, biting down gently and swirling her tongue on the thin appendage. Undyne’s throat catches for a moment before she lets out another call, louder this time. 

“Fuck, Alphys,” her words melt into unintelligible groans as she thrusts her head back onto the pillow and clenches around Alphys’s fingers. 

Alphys forges on, never stopping for a second, as Undyne reaches her peak and arches against her hand. Her mouth stays attending the fin, sucking gently until Undyne pulls away, too sensitive to stand another second of stimulation. Her hand finally withdraws after the shudder of Undyne’s climax dissipates. 

Exhausted, Alphys flops down next to Undyne to take a breather. Despite being utterly out of her comfort zone in topping, it seems to have gone quite well. She turns to ask how she’s done, but Undyne is already asleep, snoring away. She really must be exhausted, Alphys thinks. Content, she curls up and clutches her arms around her girlfriend and drifts away to the sound of distant thunder. Tomorrow would be another busy day.


End file.
